Instrumentation and Monitoring of MSE Walls Supported on the Rammed Aggregate Pier System

As part of the upgrade plans for the U.S. Highway 90 and Highway 6 Interchange, the Texas Department of Transportation (TXDOT) proposed the construction of a series of bridges and ramps. The bridge abutments and access ramps required the construction of Mechanically Stabilized Earth (MSE) retaining walls with heights of up to 8.2-m (27-feet). The weak clay foundation soils along the wall alignment presented global instability, settlement, and bearing capacity challenges. As an alternative to massive over-excavation and replacement or preloading with a surcharging, the design team and the Texas Department of Transportation selected a Rammed Aggregate Pier solution. The Rammed Aggregate Pier system (RAPs) increases the factors of safety for bearing capacity and global stability as a result of the high angle of internal friction achieved during ramming and reduces the magnitude and time of settlement by increasing the overall stiffness of the foundation soils and providing a drainage pathway for dissipation of excess pore water pressure. The performance of the Rammed Aggregate Pier-supported walls was monitored using a suite of geotechnical instrumentation consisting of vertical and horizontal inclinometers, vibrating wire piezometers, and Sondex vertical settlement gauges located near the critical sections. The instrumentation was monitored for approximately one year and indicated acceptable performance. This paper discusses the results of the monitoring program of an MSE wall supported by the Rammed Aggregate Pier system. This work is of particular significance because it is the first MSE wall support application performed in Texas and the first instrumented wall project supported on Rammed Aggregate Piers funded by the Federal Highway Administration (FHWA).